Can Finasteride or Propecia cause diabetes?

It's not entirely clear if finasteride at low doses predisposes to diabetes. It is possible. However, there is some evidence that reduction of DHT or inhibition of 5alpha reductase predisposes to changes in insulin sensitivity. It is a complex area and this should be discussed with one’s physician. 
Finasteride (Propecia and generics) inhibits the enzyme 5αR2 selectively, whereas dutasteride inhibits both 5αR1 and 5αR2.In 2010, Duskova and colleagues examined 12 men with premature balding who used Finasteride (1 mg/day) for 12 months. A hormonal profile and lipid spectrum were monitored after 4, 8 and 12 months of treatment and insulin tolerance tests were repeated after 12 months of the treatment. After treatment with finasteride the authors observed an initial increase in total cholesterol and HDL- and LDL-cholesterol, which stabilized with prolonged treatment. They found a significant decrease in glycated hemoglobin HbA1c and insulin resistance.

In 2016, studies by Hazelhurt et al suggested that Dutasteride (but not finasteride) may increase insulin resistance in the liver.


A retrospective study of 230 men in 2017 by Traish et al suggested that Dutasteride worsenen insulin resistance. Men in the study were treated with dutasteride (0.5 mg/d) for lower urinary tract symptoms due to prostate enlargement and followed-up for 3 to 3.5 years. Dutasteride user resulted in increased blood glucose, glycosylated hemoglobin A, total cholesterol, and low-density lipoprotein cholesterol levels. In addition, dutasteride treatment increased activities of liver alanine amino- transferase and aspartate aminotransferase, suggesting dysregulation of liver metabolism

A large 2019 study by Wei et al again examined the links between finasteride, Dutasteride and diabetes. The researchers compared large databases from both the UK to see if any links could be found and then analyszed data bases from Taiwan. The UK database included 8,231 men using dutasteride, 30,774 men using finasteride and compared the frequency of new onset diabetes in these individuals compared to 16, 270 patents who were using another prostate drug known as tamsulosin (Flomax). The Taiwanese database include 1251 dutasteride users, 4194 finasteride users and 86 263 tamsulosin users.

After a mean follow up time of 5.2 years in the UK database, there was a modest increased risk of type 2 diabetes for users of dutasteride (adjusted hazard ratio 1.32, 95% confidence interval 1.08 to 1.61) and finasteride (1.26, 1.10 to 1.45) compared with tamsulosin. The study carefully controlled for body mass index, other drug use, smoking, alcohol consumption, hypertension and other health and behavioral characteristics.

Results from the Taiwanese database were similar to the UK database. There was an increased risk of diabetes in dutasteride users ( 1.34, 95% confidence interval 1.17 to 1.54 ) as well as finasteride users ( 1.49, confidence interval 1.38 to 1.61 ) compared with tamsulosin).

Conclusion

Overall, this data in real terms equated to a 32 percent increased risk for developing diabetes in dutasteride 0.5 mg users and a 26 % increased risk in finasteride 5 mg users. What this means practically is that for every 1000 men treated with these drugs for 10 years, there will be 16 new cases of type 2 diabetes that can be attributed to thee drug. The authors concluded that use of finasteride at 5 mg daily or dutasteride at 0.5 mg daily may increase the risk of type 2 diabetes. The authors propose that additional monitoring might be required for men starting these drugs, particularly in those with other risk factors for type 2 diabetes.

There is no known relationship with people taking finasteride and the appearance of diabetes caused by this drug.