Consuming certain substances often causes a noticeable and sometimes alarming increase in heart rate. This physical reaction, which can feel like the heart is pounding or racing, is medically termed tachycardia, defined simply as a heart rate that is faster than normal. A rapid heart rhythm is one of the most immediate physiological effects associated with altered states of consciousness. Understanding this response involves exploring the body’s internal mechanisms that control cardiovascular function. This article will explore the specific physiological reasons behind a substance-induced fast heart rate and discuss the safety implications of this reaction.
The Body’s Stress Response
The body possesses an automatic regulatory system that constantly monitors and adjusts internal functions, including heart rate and blood pressure. This system includes the sympathetic nervous system, which initiates the body’s “fight or flight” response when a stressor is perceived. Activation prepares the body for immediate action by diverting resources to the muscles and brain.
When the sympathetic nervous system is engaged, it releases neurotransmitters like norepinephrine and the hormone epinephrine (adrenaline). These chemical messengers travel through the bloodstream and directly target the heart’s natural pacemaker, the sinoatrial (SA) node. The binding of these chemicals causes the heart to beat both faster and with greater force, a phenomenon known as a positive chronotropic effect.
This sympathetic surge also causes most blood vessels to constrict, increasing overall blood pressure. The combined effect of increased rate, increased contractility, and increased peripheral resistance is a substantial rise in cardiac output. This mechanism, designed for survival, is the same pathway that many substances hijack to produce their cardiovascular effects.
How Different Substances Affect Heart Rate
Substances that cause a rapid heart rate do so through two primary physiological pathways. Certain compounds, classified as stimulants, directly mimic or force the release of the body’s own stress chemicals. Substances like cocaine and amphetamines cause a sudden flood of norepinephrine and dopamine into the system.
This chemical surge forcefully activates the sympathetic nervous system, putting the heart into a sustained “fight or flight” mode. The direct stimulation of adrenergic receptors on the heart muscle results in a significant increase in both heart rate and blood pressure. This effect is a direct pharmacological action on the cardiovascular control centers.
The mechanism for cannabis, specifically delta-9-tetrahydrocannabinol (THC), is different and involves a secondary, compensatory reaction. THC causes blood vessels to widen (vasodilation), which leads to a temporary drop in blood pressure. The body senses this reduction and attempts to stabilize circulation by rapidly increasing the heart rate.
This compensatory speeding up of the heart is known as reflex tachycardia. The heart beats faster to ensure sufficient blood flow and oxygen delivery to the brain and organs. While both stimulants and cannabis can cause tachycardia, the former directly forces the increase, while the latter causes it indirectly as a physiological countermeasure.
Measuring and Monitoring Heart Rate
A typical resting heart rate for a healthy adult ranges between 60 and 100 beats per minute (bpm). When a person is under the influence of a substance, this rate can easily push past the 100 bpm threshold, sometimes reaching 120 bpm or higher. Knowing how to check your own pulse helps monitor the extent of the cardiovascular change.
You can safely measure your pulse by placing your index and middle fingers on the inside of your wrist (radial artery) or on the side of the neck (carotid artery). Once the throbbing sensation is located, count the number of beats that occur within 30 seconds. Multiplying this count by two provides the heart rate in beats per minute.
Regular self-monitoring helps establish a baseline and provides context for how far a substance is pushing the heart rate above its normal range. Knowing this number is a first step in evaluating potential risk.
When a Fast Heartbeat is Dangerous
While a temporary increase in heart rate is common, sustained or extreme tachycardia poses serious health risks. A rapid heart rate reduces the heart’s ability to fill completely between beats, compromising the amount of blood pumped to the body. This inefficiency increases the heart muscle’s demand for oxygen while simultaneously reducing its supply, leading to a risk of myocardial ischemia.
Extreme activation of the sympathetic system can also trigger an irregular heart rhythm (arrhythmia), disrupting the heart’s electrical signaling. Certain rhythms are disorganized and potentially life-threatening, preventing the heart from pumping effectively. The combined strain of a rapid heart rate and high blood pressure can precipitate a hypertensive crisis, a medical emergency that can damage organs.
Immediate medical attention is necessary if a rapid heart rate is accompanied by specific warning signs:
- Chest pain or discomfort.
- Difficulty breathing or shortness of breath.
- Sudden dizziness.
- Fainting.
A persistent heart rate above 120 to 140 bpm, especially at rest, warrants professional evaluation to prevent serious cardiovascular complications.