Being “high” from many psychoactive substances often causes a noticeable increase in heart rate, medically termed tachycardia. This accelerated heart rhythm is a direct physiological reaction to the chemical compounds entering the body, not simply a sensation based on anxiety. Substances that affect brain chemistry frequently impact the cardiovascular system, leading to a faster and harder heartbeat.
The Physiological Cause of Heart Rate Changes
The primary driver behind substance-induced heart rate changes is the Autonomic Nervous System (ANS), which controls involuntary functions like breathing and heart rate. Psychoactive compounds often directly stimulate the Sympathetic Nervous System (SNS), known as the “fight or flight” response. This activation prepares the body for immediate action by releasing catecholamines, primarily epinephrine (adrenaline) and norepinephrine.
These neurotransmitters bind to specialized beta-adrenoreceptors on the heart muscle cells. The binding acts like a chemical trigger, forcing the heart to beat both faster and with greater force, significantly increasing cardiac output. This heightened workload is a direct consequence of the chemical manipulation of the body’s natural stress response pathways. The increase in heart rate is the body’s mechanical reaction to being flooded with chemical messengers that mimic danger.
Substances Known to Affect Heart Rhythms
Different classes of substances cause tachycardia through distinct pharmacological mechanisms. Stimulant compounds, such as cocaine and amphetamines, are the most direct cause of a rapid heart rate. They flood the system with norepinephrine and block its reuptake, intensifying the SNS response. This activation constricts blood vessels, spiking blood pressure and forcing the heart to work harder against increased resistance.
Other substances, like cannabis, cause an accelerated heart rate through a more indirect, reflexive mechanism. Cannabis often causes vasodilation (the widening of blood vessels) and a resulting drop in blood pressure. The heart then reflexively speeds up to compensate for this sudden drop, attempting to maintain sufficient blood flow to the brain and other organs.
Hallucinogens and psychedelic substances, such as MDMA or LSD, also affect heart rate due to their interaction with serotonin receptors. These interactions can lead to sympathomimetic effects—mimicking the sympathetic nervous system—resulting in dose-dependent increases in heart rate and blood pressure. The experience of anxiety or paranoia associated with these substances can further contribute to the heart rate increase, creating a feedback loop of psychological and physiological stress.
Recognizing When a Fast Heart Rate Becomes Dangerous
While a temporary increase in heart rate might be uncomfortable, it can quickly become medically concerning if it turns into an arrhythmia or an irregular beat. Vulnerable populations face a higher risk of serious complications, including individuals with pre-existing heart conditions like hypertension, coronary artery disease, or prior heart attacks. Even a single instance of substance use can cause acute heart issues.
It is important to recognize specific warning signs that necessitate immediate medical intervention, moving beyond simple palpitations. Symptoms that should prompt a call for emergency help include:
- Chest pain or discomfort.
- Significant difficulty breathing.
- Feeling dizzy or lightheaded.
A heart rate that remains excessively fast or feels chaotic and irregular for a prolonged period also warrants professional medical attention.
Long-Term Cardiac Risks
Chronic or repeated substance-induced tachycardia places a continuous strain on the heart muscle. This persistent overwork can lead to long-term implications, including damage to the cardiac tissue, or the development of conditions like cardiomyopathy (weakening of the heart muscle).
The combination of a rapid heart rate and constricted blood vessels creates an imbalance between the heart’s increased need for oxygen and the reduced supply. This raises the risk of a heart attack or stroke.