Once your PET scan is finished, you can eat and drink normally right away. The hours of fasting and dietary restrictions that preceded the scan are over the moment you leave the imaging table. The single most useful thing you can do afterward is drink plenty of water, because the radioactive tracer leaves your body primarily through your urine, and staying well-hydrated speeds that process along. Beyond hydration, there are a few practical considerations worth knowing, especially if you are breastfeeding, managing diabetes, or wondering how long the tracer lingers.
Why Water Is the Top Priority
The tracer used in most PET scans is a radioactive sugar called fluorodeoxyglucose, or FDG. After the scan, your body clears FDG and similar tracers rapidly, with the primary exit route being through the kidneys and urinary tract. The tissues that absorb the highest residual dose tend to be the bladder wall and parts of the intestinal lining, simply because the tracer passes through them on the way out.1PubMed Central. Pilot study of PET imaging of 124I-iodoazomycin galactopyranoside (IAZGP), a putative hypoxia imaging agent, in patients with colorectal cancer and head and neck cancer – Section: RESULTS That is exactly why clinicians encourage you to drink extra fluids and empty your bladder frequently in the hours that follow.
In clinical protocols designed to clear FDG from the pelvic region as quickly as possible, patients have been given roughly a liter to a liter and a half of water by mouth and told to urinate at least three times in the period after their scan.2PubMed Central. Pet/Ct Forced diuresis and dual-phase 18 F-fluorodeoxyglucose-PET/CT scan for restaging of urinary bladder cancers You do not need to follow that exact volume as a rigid prescription, but it gives a sense of what “drink plenty of water” actually means in practice. For most people, aiming for six to eight extra glasses of water over the four to six hours after a scan is a reasonable target. Each trip to the bathroom flushes more tracer out of your system and reduces the radiation dose to your bladder lining.
Plain water works fine. If you find it difficult to drink that much water on its own, herbal tea, diluted juice, or other non-caffeinated drinks accomplish the same thing. The goal is simply to keep urine flowing.
Returning to Normal Meals
Before a PET scan you are typically asked to fast for four to six hours and avoid sugary foods and drinks, because FDG competes with glucose for uptake in your cells. High blood sugar at the time of injection can compromise image quality. None of that matters once the scan is complete. The tracer has already been distributed and imaged, so eating will not affect your results retroactively.
Most people feel genuinely hungry after the combined fasting and the stress of the appointment, so go ahead and eat whatever appeals to you. There is no specific “post-PET diet.” A normal balanced meal is the simplest approach. If you skipped breakfast for a morning scan, lunch can be anything you would ordinarily eat. Some people feel mildly fatigued or lightheaded after fasting, and a meal that combines protein, some carbohydrates, and fats will help restore your energy faster than a candy bar or a bag of chips alone.
One practical note: because you are also trying to drink a lot of extra water, having a meal at the same time can actually help. Eating slows the rate at which water passes through your stomach, which some people find more comfortable than chugging water on an empty stomach and feeling bloated.
When You Can Have Caffeine Again
Whether caffeine was restricted before your scan depends on the type of PET study. For a standard FDG PET scan used in cancer staging, most facilities do not require you to cut out caffeine beforehand. For cardiac PET studies, however, caffeine is typically restricted for 12 to 24 hours before the scan because it blocks the adenosine receptors that certain cardiac stress agents target. Caffeine competes directly at those receptors in a dose-dependent way, and its biological half-life is around five hours, meaning it hangs around long enough to interfere with the test if consumed too close to scan time.3Journal of Nuclear Medicine. Caffeine Occupancy of Human Cerebral A1 Adenosine Receptors: In Vivo Quantification with 18F-CPFPX and PET
Once the scan is done, you can have coffee, tea, or any other caffeinated drink whenever you like. The restriction exists entirely to protect image quality during the scan itself, and that window has closed. If you are a regular coffee drinker who skipped your morning cup, that post-scan coffee is safe and may help with the headache that caffeine withdrawal sometimes causes. Just keep in mind the hydration goal: coffee is a mild diuretic, which actually helps with flushing the tracer, but it can also make you feel less thirsty than you really are. Chase it with extra water.
Alcohol After a PET Scan
There is no specific prohibition on alcohol after a PET scan from a radiopharmaceutical standpoint. The tracer and alcohol do not interact in any clinically meaningful way. That said, there are common-sense reasons to hold off for a few hours. You have been fasting, possibly since the night before, and alcohol on an empty or recently empty stomach hits harder and faster. You are also trying to hydrate aggressively, and alcohol works against that goal by suppressing the hormone that helps your kidneys reabsorb water.
If you want a glass of wine with dinner that evening, that is fine for most people. But pounding drinks right after leaving the imaging center is not ideal if your goal is efficient tracer clearance. Eat first, hydrate well, and then resume your normal routine.
Managing Blood Sugar if You Have Diabetes
Fasting before a PET scan poses a specific challenge for people with diabetes, particularly those on insulin or medications that lower blood sugar. Facilities generally require blood glucose to be below a certain threshold before they will proceed with the injection; levels above roughly 150 to 200 mg/dL (about 8.3 to 11.1 mmol/L) can degrade image quality enough that some centers will reschedule the scan.4Journal of Nuclear Medicine Technology. Could Different Hydration Protocols Affect the Quality of 18F-FDG PET/CT Images? Getting through the scan means you have navigated the tricky part.
After the scan, resume your normal eating and medication schedule as soon as possible. If you delayed an insulin dose or skipped a meal to meet the fasting requirement, your blood sugar may swing once you start eating again. Check your glucose before your first post-scan meal and adjust your insulin or medication accordingly, following whatever plan your endocrinologist or primary care provider has outlined. Carry a fast-acting glucose source with you to the appointment in case your sugar drops while you are still at the facility; some imaging centers will not let you eat in the uptake room, but the staff should be able to help if you experience hypoglycemia symptoms.
One thing worth knowing: the fasting period is the only diabetes-specific concern. There is no reason to modify your diet in any special way for days before or after the scan, beyond whatever your usual diabetes management requires.
Breastfeeding After a PET Scan
If you are nursing, the radiotracer can appear in breast milk in small amounts, and guidelines recommend a temporary interruption. For an FDG PET scan, a 12-hour break from breastfeeding is the standard recommendation.5Journal of Nuclear Medicine Technology. Duration of Breastfeeding Interruption in Nuclear Medicine Procedures – Section: RESULTS During that 12-hour window, you should express milk at least three times and discard it rather than feeding it to your baby.6PubMed. Excretion of radionuclides in human breast milk after nuclear medicine examinations. Biokinetic and dosimetric data and recommendations on breastfeeding interruption Pumping and discarding serves two purposes: it keeps your supply up and it removes the milk that contains the highest concentration of tracer.
The 12-hour timeframe is designed to keep the infant’s radiation exposure below 1 mSv, a threshold considered negligible.6PubMed. Excretion of radionuclides in human breast milk after nuclear medicine examinations. Biokinetic and dosimetric data and recommendations on breastfeeding interruption After the 12 hours have passed, you can nurse normally. If you know the scan is coming, pump and store enough milk in advance to cover at least two or three feedings so your baby has a supply during the interruption.
It is worth noting that the 12-hour interruption applies specifically to FDG. Other nuclear medicine procedures use different radiotracers with different half-lives and excretion patterns, and some do not require any breastfeeding interruption at all. If you are scheduled for a non-FDG scan, ask the nuclear medicine team for the recommendation specific to the tracer being used.
Reducing Radiation Exposure to People Around You
After the injection, you are mildly radioactive for several hours. The radiation dose you emit drops quickly because fluorine-18, the isotope in FDG, has a physical half-life of about two hours. By six to eight hours after injection, the combination of radioactive decay and urinary excretion has brought your radiation levels down to a small fraction of what they were at peak.
For practical purposes, most imaging centers advise keeping some distance from pregnant women and young children for the remainder of the day. “Some distance” usually means avoiding prolonged close contact like holding a baby on your lap for an extended period or lying next to a pregnant partner for hours. Brief interactions, like picking up a child or sitting across a table, are not a concern. If you have an infant at home, having another caregiver handle diaper changes and feedings for the rest of the day is a reasonable precaution.
Drinking plenty of water and urinating frequently, as already discussed, is the single most effective thing you can do to reduce the total time you are emitting radiation. Each bathroom trip literally flushes radioactive material out of your body. Washing your hands thoroughly after using the toilet is also good practice, not because the radiation on your hands is dangerous but because it minimizes trace contamination on surfaces others might touch.
Foods and Supplements That Do Not Matter
A quick internet search will turn up suggestions about eating antioxidant-rich foods, taking iodine supplements, or consuming specific “detox” juices after a PET scan. None of these have evidence behind them for FDG PET specifically. FDG is not iodine-based, so iodine supplements are irrelevant (those are relevant to certain thyroid-related nuclear medicine procedures, not standard PET scans). Antioxidants do not accelerate the physical decay of a radioactive isotope or change how quickly your kidneys filter it out. The isotope decays on its own fixed schedule regardless of what you eat.
Similarly, there is no need for a special “radiation recovery” diet. Your body did not absorb a large dose of radiation during a diagnostic PET scan. The effective dose from a typical FDG PET/CT is in the range of a few years’ worth of natural background radiation, delivered over a short time. It is something to be mindful of over a lifetime of repeated imaging but not something that calls for nutritional intervention after a single scan.
If you take daily supplements or medications that were paused for the scan (some facilities ask patients to hold certain drugs), resume them with your next meal unless your doctor says otherwise. Metformin, a common diabetes drug, is sometimes held before contrast-enhanced CT portions of a PET/CT study. If that applies to you, your imaging team should have given specific instructions on when to restart it, typically after confirming that your kidney function is stable.
If You Had Sedation or Anesthesia
Most adult PET scans do not require sedation, but some patients, including young children and people with severe claustrophobia or movement disorders, may receive a sedative or general anesthesia to stay still during the scan. If you were sedated, post-scan eating and drinking follow the recovery guidelines for anesthesia rather than anything specific to the radiotracer. That usually means starting with clear liquids once you are alert enough to swallow safely, then progressing to solid food as tolerated. Nausea is the most common issue after sedation, and forcing a full meal before you feel ready can make it worse.
For children who were sedated, the pediatric recovery team will give specific instructions about when and what to offer. Do not let a child who is still drowsy drink from an open cup or eat anything they could choke on. Once the sedation has fully worn off and the child is alert and asking for food, normal meals are fine.
What About Kidney Problems
Because FDG clears through the kidneys, people with impaired kidney function may process the tracer more slowly. Some research protocols exclude patients with renal failure from standard imaging studies for this reason.4Journal of Nuclear Medicine Technology. Could Different Hydration Protocols Affect the Quality of 18F-FDG PET/CT Images? If you have chronic kidney disease, the “drink lots of water” advice still applies in principle, but the volume needs to be adjusted to your fluid restrictions. Overloading your kidneys with a liter of water in an hour could be harmful if you are on a fluid-restricted diet.
Talk to your nephrologist or the nuclear medicine team about a hydration plan that balances tracer clearance with your kidney capacity. In most cases, moderately increasing your fluid intake within your allowed limits and urinating as often as you comfortably can is sufficient. The tracer will still decay on its two-hour physical half-life schedule regardless of how quickly your kidneys work, so even with slower clearance, the radiation exposure is time-limited.
How Long Until Everything Is Back to Normal
For the vast majority of people, “back to normal” happens within a few hours of leaving the imaging center. By dinner that evening, the tracer has largely decayed and been excreted, your blood sugar has normalized, and there is nothing about the scan that lingers in your body in any meaningful way. The only exception is if you are breastfeeding, in which case the 12-hour pump-and-discard window may stretch into the following morning depending on when your scan was scheduled.
There is no need to alter your diet the next day or the day after. You do not need follow-up blood work related to the tracer itself (though your doctor may order labs for other reasons related to whatever condition prompted the scan). If you feel perfectly fine the moment you walk out the door, that is because you are perfectly fine. A PET scan is a diagnostic tool, not a treatment, and the tracer dose is deliberately kept as low as possible while still producing useful images. Eat what you like, drink extra water for the rest of the day, and carry on.