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Abdul Mannan: How SSRIs Might Affect Platelet Function
Abdul Mannan/LinkedIn
Mar 28, 2026, 18:48

Abdul Mannan: How SSRIs Might Affect Platelet Function

Abdul Mannan, Consultant Hematologist at Betsi Cadwaladr University Health Board, shared a post on LinkedIn:

“Your SSRI might be affecting how your platelets work.

Most people don’t know this.

Most doctors don’t talk about it.

But the biology is real.

Here’s what’s happening:

  • Platelets don’t make serotonin. They absorb it from blood and store it. This stored serotonin helps activate platelets during clotting.
  • SSRIs block the serotonin transporter (SERT). Over time, platelets may have less serotonin available.
  • The SLC6A4 gene controls how active your SERT is. Some people carry the high-activity L(A)/L(A) genotype. Others have lower-activity types: S or L(G).
  • In studies, patients with lower-activity genotypes (fewer than 2 L(A) alleles) showed longer PFA-100 closure times and prolonged bleeding times by about 2.3 minutes on SSRIs.
  • In high-activity genotypes, SSRIs caused little or no change in bleeding time.

So genetics may modulate how much your platelets are affected by these drugs.

But before you order a gene panel – the clinical message is more grounded than that.

  • The biology is plausible.
  • The evidence is small and mixed.
  • Not all studies agree.
  • Routine genetic testing is not currently recommended.

The bigger bleeding risks remain age, aspirin and NSAID use, anticoagulants, and prior GI bleeding.

This is a conversation worth having with patients on SSRIs who also have other bleeding risk factors.

Have you seen unexpected bleeding in a patient on SSRIs?

How did you approach it?”

Abdul Mannan

More posts featuring Abdul Mannan on Hemostasis Today.

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