Yes, anticholinergics increase heart rate. This is one of the most predictable effects of these drugs, and it happens because they block the nerve signals that normally keep your heart rate in check. The effect ranges from a barely noticeable bump of a few beats per minute with common antihistamines to dramatic increases of 50 or more beats per minute with potent anticholinergics like atropine.
How Anticholinergics Speed Up the Heart
Your heart doesn’t beat at its maximum speed by default. The vagus nerve, which runs from your brainstem to your heart, constantly releases a chemical messenger called acetylcholine that acts like a brake. This messenger binds to M2 receptors concentrated in the sinoatrial node, the heart’s natural pacemaker, slowing the rate at which it fires. Without this brake, your resting heart rate would sit closer to 100 beats per minute instead of the typical 60 to 80.
Anticholinergic drugs block acetylcholine from reaching those M2 receptors. With the brake removed, the heart speeds up. This is called a positive chronotropic effect. The clearest real-world evidence comes from heart transplant patients: because their vagus nerve connection to the heart is severed during surgery, they lose this braking mechanism entirely and tend to have higher resting heart rates and reduced heart rate variability.
Which Drugs Have This Effect
Many common medications carry anticholinergic activity, some obviously and some as a side effect you might not expect. The strength of the heart rate increase depends on how potent the drug’s anticholinergic action is and how much you take.
- Atropine is the most well-known example. At standard doses (roughly 0.5 mg in an adult), it can increase heart rate by 20 to 72 beats per minute. At higher doses, heart rate can climb by 50 to 92 beats per minute, sometimes exceeding 120.
- Diphenhydramine (Benadryl) is the over-the-counter antihistamine most associated with heart rate changes. At normal doses, the effect is mild. In overdose situations (typically above 500 mg, far beyond the recommended 25 to 50 mg), 75% of patients had heart rates above 90 beats per minute and 25% exceeded 120.
- Overactive bladder medications like oxybutynin and tolterodine are prescribed specifically for their anticholinergic effects on the bladder, but they act on the heart too.
- Tricyclic antidepressants and certain older antipsychotics carry significant anticholinergic activity, which contributes to the tachycardia commonly reported as a side effect.
- Some motion sickness and anti-nausea drugs, including scopolamine, directly block the same receptors.
The heart rate increase from a single therapeutic dose of a mild anticholinergic (like one Benadryl tablet) is usually small enough that most people won’t notice it. Stronger anticholinergics or higher doses produce more obvious effects.
Recognizing Anticholinergic Side Effects
A faster heart rate from anticholinergics rarely shows up in isolation. Because acetylcholine is active throughout your body, blocking it produces a cluster of symptoms that tend to appear together. Medical trainees learn these through the mnemonic “red as a beet, dry as a bone, blind as a bat, mad as a hatter, hot as a hare, full as a flask.” In plain terms, that translates to flushed skin, dry mouth, dilated pupils with blurry vision, confusion or agitation, elevated body temperature, and difficulty urinating.
One useful distinction: anticholinergic-driven tachycardia looks similar to what happens with stimulants like amphetamines or cocaine. The key difference is sweat. Stimulants make you sweat profusely. Anticholinergics shut down sweating because the same receptors control your sweat glands. If your heart is racing and your skin is dry and flushed, anticholinergic effects are the more likely explanation.
At toxic levels, particularly with diphenhydramine, the heart rate increase can progress beyond simple tachycardia to abnormal rhythms, including wide-complex tachycardia and prolonged QT intervals on an ECG. These are serious findings that require emergency attention.
Why Older Adults Are More Vulnerable
The heart rate effects of anticholinergics hit older adults harder for a straightforward reason: aging reduces the autonomic nervous system’s ability to compensate. When a younger person’s heart speeds up from an anticholinergic drug, other regulatory mechanisms can partially offset the change. In older adults, that reserve is diminished, so the same dose produces a larger and less predictable cardiovascular response.
This is part of a broader pattern. Anticholinergics are associated with increased risks of falls, cognitive impairment, and higher mortality in older populations. Clinical guidelines like the Beers Criteria and STOPP criteria specifically flag anticholinergic medications as potentially inappropriate for older adults. Pharmacists and physicians are increasingly encouraged to assess total “anticholinergic burden,” the combined effect of all anticholinergic medications a patient takes, since many people are on several at once without realizing the cumulative impact.
The cognitive effects deserve special mention here. In older adults, anticholinergics can cause confusion, delirium, and memory problems that compound the cardiovascular risks. Someone whose heart is beating faster while also feeling disoriented faces a meaningfully higher fall risk.
When the Heart Rate Increase Is Intentional
Not all anticholinergic-driven heart rate increases are unwanted side effects. Atropine is a frontline treatment for bradycardia, a dangerously slow heart rate. In emergency settings, it works by doing exactly what this article describes: blocking the vagal brake so the heart can speed up to an adequate rate. Clinical data shows that even small doses of atropine (around 0.4 to 0.6 mg for a typical adult) reliably raise heart rate by 20 or more beats per minute, with the effect appearing within seconds when given intravenously.
This intentional use illustrates that the heart rate effect isn’t inherently dangerous. It becomes a problem when it’s unexpected, when it pushes an already-fast heart rate higher, or when it occurs in someone whose cardiovascular system can’t handle the extra demand.
Practical Takeaways
If you’re taking an anticholinergic medication and notice your heart beating faster, the drug is a plausible explanation, especially if you also have dry mouth or blurry vision. A mild increase at therapeutic doses is common and usually not harmful in otherwise healthy people. The concern grows with higher doses, multiple anticholinergic drugs taken together, older age, or pre-existing heart conditions. If you’re experiencing a resting heart rate consistently above 100 while on one of these medications, that’s worth discussing with whoever prescribed it, as dose adjustments or alternative drugs with less anticholinergic activity are often available.