Scientists don’t know for sure if the use of marijuana causes erectile dysfunction. https://pubmed.ncbi.nlm.nih.gov/29523476/
We do know that there are cannabinoid receptors in the smooth muscle of the penis. Anything that slows down the process of blood getting into the penis can cause ED, so there is at least a theoretic reason that smoking pot might make getting hard more challenging physiologically.
This would suggest that some men, particularly those that have more of a mental block than vascular insufficiency probably get more benefit from THC than harm.
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Eat heart-healthy foods.
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Exercise
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Quit smoking.
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Lose weight.
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Focus on getting rid of central obesity. (A hidden bonus: your penis will look bigger!)