From the Research
Benadryl (diphenhydramine) should be used with caution in patients with a history of brain clots, and alternative non-sedating antihistamines are generally safer options. The most recent and highest quality study, 1, published in 2022, compared direct oral anticoagulants (DOACs) to warfarin in the treatment of cerebral venous thrombosis, but did not directly address the use of antihistamines like Benadryl. However, considering the potential anticholinergic effects of Benadryl, which can affect blood flow and increase the risk of clotting, it is essential to exercise caution.
For patients with a history of brain clots, alternative non-sedating antihistamines like Claritin (loratadine), Zyrtec (cetirizine), or Allegra (fexofenadine) are generally safer options as they have fewer anticholinergic effects and less impact on cerebral blood flow. The standard adult dose for these alternatives is typically 10mg once daily for Claritin or Zyrtec, or 180mg once daily for Allegra.
If you're currently on blood thinners or other medications for your condition, it's especially important to check with your doctor before taking any antihistamine, as interactions could occur. The underlying concern is that medications with strong anticholinergic effects like Benadryl might theoretically increase the risk of clotting or interfere with medications used to prevent clots.
Some studies, such as 2 and 3, provide information on the diagnosis and management of cerebral venous thrombosis and stroke, but do not directly address the use of antihistamines in patients with a history of brain clots. An older study, 4, compared the central nervous system effects of H1-receptor antagonists in the elderly, suggesting that newer H1-receptor antagonists like cetirizine and loratadine may cause less central nervous system dysfunction than older H1-receptor antagonists like diphenhydramine.
In summary, while there is no direct evidence addressing the safety of Benadryl in patients with a history of brain clots, it is recommended to use alternative non-sedating antihistamines and consult with a healthcare provider before taking any antihistamine, especially if you are currently on blood thinners or other medications for your condition, as noted in 1.