Biogen (NASDAQ:BIIB) faces continued challenges for several of its current products. However, the company also now has Alzheimer's disease drug Aduhelm, which could be a huge commercial success. In this Motley Fool Live video, recorded on July 19, 2021, healthcare and cannabis bureau chief Corinne Cardina and Motley Fool contributor Keith Speights answer a viewer's question about whether now is a good time to buy Biogen stock.

Corinne Cardina: This person, Fan of Brian and Brian but not Brian, I believe they are trying to stir the pot in terms of all of our Brians.

Keith Speights: We've a lot of Brians at the Fool.

Cardina: I'm like, who's who? But anyways, very funny. "With all the drama on Biogen, do you think it is now a good time to invest? If it brings them billions, it sounds like a yes. What do we think? Especially, do we know anything about the valuation side?"

That's interesting.

Speights: Yeah. My take is that Biogen is a better stock to buy now than it's been in a long, long time. I have not been a fan of Biogen for the last few years. As I mentioned earlier in our segment, Biogen's multiple sclerosis franchise sales are declining, that's its flagship franchise, its spinal muscular atrophy drug sales are declining. Biogen absolutely needed a win and it pulled it out. It pulled out a win here.

Opinions vary as to what the sales for Aduhelm will be. I don't think they're going to be at the top end of the ranges that you hear. I don't think they're going to be at the low end either. I think it's going to be somewhere in between.

I would say Biogen is a stock to consider buying. I'm not going to just say, "Oh, buy it," but I think it's a stock to consider buying. If you think that -- as I think -- that more doctors are going to prescribe Aduhelm for Alzheimer's disease than won't.

Cardina: Let me ask you, what is behind the MS franchise problems? Is there a better MS drugs on the market? What's going on with that?

Speights: A lot of the drugs are getting old in the tooth and are facing some generic competition and facing newer competition. That's the main thing there is that it's just, these are older drugs. and they've started to run their course.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.