One of the relatively rare side effects of venlafaxine is that it may cause bruising or bleeding. It can reduce the function of blood platelets leading to an increased risk of bruising or bleeding. Therefore, your doctor may wish to do blood tests, particularly if you have been taking Venlafaxine tablets for a long time.
We also need to bear in mind the possibility of drug interactions. For example, SSRIs may increase the risk of bleeding, especially when the person is taking other medications that increase the risk of bleeding, such as:
- Nonsteroidal anti-inflammatory drugs (NSAIDs),
- Aspirin,
- Warfarin,
- Other blood thinners.
Let us look at the mechanism of action of SSRIs (serotonin specific reuptake inhibitors) and SNRIs (serotonin norepinephrine reuptake inhibitors).
Apart from its effects on the central nervous system, serotonin (5-hydroxytryptamine, 5-HT) also assists with platelet activation and aggregation. Platelets themselves do not synthesize 5-HT but rely on the uptake of 5-HT, via the serotonin transporter, from the bloodstream. Once a platelet receives 5-HT, it is stored within the dense granules of the platelet. Upon platelet activation, the stored 5-HT is released with other aggregation factors such as collagen and assists with proper aggregation.
Medications that inhibit 5-HT reuptake, such as SSRIs and SNRIs, act as an antagonist of the serotonin transporter necessary to transport 5-HT into the platelet, leading to a lower concentration of 5-HT within the platelet. The decrease in the platelet 5-HT level, therefore, leads to bleeding tendencies. Another interesting and relevant finding is that medications with a higher affinity for the serotonin transporter, such as fluoxetine, have been found to have a higher risk of bleeding compared to those with a lower affinity such as venlafaxine.
In conclusion, do seek help from your doctor as soon as possible. He or she will obtain a complete history of the medications that you have been taking. Blood tests may be ordered. Switching to another medication may also be considered.
