Finasteride and Venlafaxine (Effexor) Drug Interaction Assessment

No clinically significant drug interaction exists between finasteride and venlafaxine (Effexor). 1

Evidence for Lack of Interaction

Finasteride does not appear to affect the cytochrome P450-linked drug metabolizing enzyme system, which is the primary pathway for potential drug interactions 1
The FDA drug label specifically states that "no drug interactions of clinical importance have been identified" with finasteride 1
Finasteride has been concomitantly used with numerous medications in clinical studies without evidence of clinically significant adverse interactions 1
Finasteride undergoes extensive hepatic metabolism to essentially inactive metabolites, with a terminal elimination half-life of 4.7 to 7.1 hours 2
Finasteride is highly specific in its action, targeting the 5-alpha-reductase enzyme primarily in the prostate gland, scalp, and genital skin, which limits its potential for systemic drug interactions 2

Finasteride is a synthetic 4-azasteroid that specifically inhibits 5-alpha-reductase, converting testosterone to dihydrotestosterone (DHT) 3
It is well absorbed after oral administration with approximately 90% plasma protein binding 3
Finasteride is primarily used for benign prostatic hyperplasia (BPH) and androgenetic alopecia (male pattern hair loss) 4
The recommended dosage for BPH is 5 mg once daily, while 1 mg daily is used for hair loss 3

While there is no direct interaction between finasteride and venlafaxine, there is one case report of a patient with BPH who experienced urinary incontinence after starting venlafaxine while on stable treatment with tamsulosin and finasteride 5
This isolated case report suggests the urinary symptoms were related to venlafaxine rather than an interaction with finasteride 5
Finasteride has been associated with certain adverse effects including erectile dysfunction, decreased libido, and decreased volume of ejaculate, but these are not related to drug interactions 3
Some patients on finasteride report sleep disturbances including insomnia, which could theoretically overlap with venlafaxine's side effect profile, but this does not constitute a pharmacological interaction 6

When prescribing both medications concurrently, standard monitoring for the known side effects of each medication individually is sufficient 1, 2
No special dose adjustments are necessary when using finasteride and venlafaxine together 1
Patients should be informed about the potential side effects of each medication separately rather than concerns about interactions 3

Attributing side effects of one medication to an interaction between the two medications when they are likely independent effects 2, 3
Discontinuing beneficial therapy unnecessarily due to unfounded concerns about drug interactions 1
Failing to recognize that symptoms like sleep disturbances could be related to either medication independently rather than an interaction 6