Do Antidepressants Affect Heart Rate Variability?
Depression itself lowers HRV, which makes the medication question harder to isolate than it first appears.
This piece covers what controlled research has found about antidepressant use and heart rate variability, drawing on trials comparing SSRIs, venlafaxine, mirtazapine, and quetiapine combinations. It does not cover HRV in untreated depression alone, cardiac patients on antidepressants, or long-term use beyond the windows these trials measured.
Research comparing antidepressant classes has found that HRV changes during treatment are not uniform across drugs. One trial found venlafaxine and mirtazapine were followed by a further decline in total power HRV over four weeks, while a separate study found that SSRI use alone was not significantly linked to lower HRV, though combining an antidepressant with quetiapine was. The honest read is that class and combination matter more than the blanket idea of 'antidepressants and HRV' as one relationship.
The question behind the wearable drop
Someone starts a new antidepressant, keeps wearing their tracker out of habit, and notices their morning HRV number has been sliding for weeks. The obvious question is whether the medication is doing that, or whether it's the depression or anxiety that was already there before the prescription. It's a reasonable thing to wonder about, because reduced HRV has been described as a physiological marker tied to the same autonomic patterns that show up in mood disorders. Separating a drug effect from an illness effect on a single trend line is not simple.
The research that exists on this doesn't treat 'antidepressants' as one thing. It splits by class, and the findings split right along with it.
2 studies
- In depressed patients treated with venlafaxine or mirtazapine, HRV total power declined further during the treatment period, on top of already-reduced HRV compared with non-depressed controls. Medication type and whether patients had achieved remission after four weeks were not related to the size of this decline.
- Comparing patients on no antidepressant, an SSRI (sertraline or escitalopram), venlafaxine or mirtazapine, or an antidepressant plus quetiapine, the augmentation group had the lowest HRV values. Age and quetiapine use were negatively correlated with HRV measures, but antidepressant use alone was not found to have a significant autonomic effect in this sample.
Why the two main studies don't agree on 'antidepressants' as a category
The venlafaxine and mirtazapine trial measured a specific window, comparing HRV before treatment, after a washout period, and again at 14 and 28 days of treatment, in both depressed patients and non-depressed controls. It found that depression on its own tracked with reduced HRV, and that HRV total power declined further as treatment continued, regardless of whether patients responded to the medication.
The Pharmacopsychiatry study took a different approach, comparing four medication groups directly against each other rather than tracking one group over time. SSRIs alone didn't stand out as the driver of lower HRV in that comparison. The standout group was the one combining an antidepressant with quetiapine, where age and quetiapine use were the factors that correlated with lower HRV markers, not the antidepressant itself.
Read together, these aren't contradictory so much as they're answering slightly different questions. One is asking what happens to HRV as venlafaxine or mirtazapine treatment progresses. The other is asking which medication group has the lowest HRV at a single comparison point, and in that comparison the antipsychotic addition looks more consequential than the antidepressant class. Anyone trying to map a single wearable trend onto either of these designs should keep in mind that neither study was built around free-living, consumer HRV tracking. There's a broader pattern underneath both of them, though, which is how depression and anxiety themselves relate to HRV independent of any medication, something I cover more directly in the piece on whether HRV reflects depression.
Neither trial used consumer wearables. The Terhardt et al. study measured supine and upright HRV in a clinical setting after a structured washout period, and the Huang et al. study compared psychiatric patients across medication groups at a single point. Neither tells you what a nightly PPG-based HRV reading on a smartwatch would show for the same drug groups, and neither followed patients for more than a few weeks.
What this doesn't settle
Nothing in these two trials establishes a mechanism for why venlafaxine or mirtazapine would track with declining HRV while SSRIs alone did not stand out in the other comparison. The abstracts describe the pattern, not the physiology behind it. Whatever autonomic mechanisms are proposed for HRV more broadly, including the link between autonomic imbalance and cardiovascular risk factors described in general HRV review literature, would need to be tested directly in antidepressant users to know if the same pathway applies.
Sample sizes in both trials were modest, split across several medication subgroups, which limits how confidently any single class can be singled out. And both studies were done in people already diagnosed with depression, anxiety, or related psychiatric conditions. None of this speaks to what antidepressants would do to HRV in someone without a mood disorder, a comparison that hasn't been run in this evidence set.
For anyone trying to interpret a single number rather than a trend, what counts as a good HRV number varies enough between individuals that a medication-related shift is easier to spot as a trend over weeks than as a single reading.
Neither study followed patients long enough to say whether an initial HRV decline during the first weeks of treatment persists, reverses, or stabilizes months later. Anyone comparing wearable data across a longer medication history has no direct trial evidence covering that time frame here.
Common questions
Do SSRIs lower HRV?
In the comparison across medication groups in the Huang et al. study, SSRI use alone (sertraline or escitalopram) was not found to have a significant association with HRV, while combining an antidepressant with quetiapine was linked to the lowest HRV values in that sample.
Do venlafaxine and mirtazapine affect HRV differently than SSRIs?
The Terhardt et al. trial found that HRV total power declined further during treatment with venlafaxine or mirtazapine, on top of the reduced HRV already seen in depressed patients versus controls. That decline was not tied to whether patients reached remission.
Could low HRV on my wearable be from depression itself rather than medication?
The Terhardt et al. study found that depressed patients had reduced HRV and increased heart rate compared with non-depressed controls before treatment began, so a baseline difference tied to the condition itself is part of the picture independent of any drug.
Is quetiapine the bigger factor rather than the antidepressant?
In the Huang et al. comparison, the group combining an antidepressant with quetiapine had the lowest HRV, and quetiapine use (along with age) was negatively correlated with HRV measures, while antidepressant use by itself was not found to be significant in that sample.