Valdenafil (Levitra) has shown some effect on ALS [1]. Coincidentally, the related sildenafil (Viagra) was identified through computer-aided research as a drug of interest in Alzheimer's prevention. [2]
It has very interesting effects. You'll find that it helps with ingrown hairs. They'll begin to get out on their own, within hours of taking it orally and in general become very eager to come out with simple hand motions.
Someone should look into it. Consistent effect. I looked into it years ago and indeed PDE5 inhibition has something to do with ingrown hairs.
A very large, six-year study in US Veterans Administration patients (N = tens of thousands), published in April, has shown that having had a recent Tdap vaccine predicts a 40% decrease in risk of dementia.
It is hard to imagine a confounder with such an effect size. (I got my Tdap booster right away, because why not?) The result was so surprising that a completely independent cohort was checked and showed an effect of the same size.
No one knows yet which component of the Tdap vaccine administered is responsible for the result.
The Viagra effect size reported was 60%. I doubt aspirin would show 60% against headache. (Unrelated, Viagra sometimes causes headache :)
1. https://www.sciencedirect.com/science/article/pii/S096999611... 2. https://www.everydayhealth.com/alzheimers-disease/viagra-may...