Clen sides are brutal and not worth it.
Clen has a 36 hour half-life, which means it's peak of effectiveness is 18 hours after you take it. Dosing it sucks, and you can literally go days without sleeping on it. Also, having to run Ketoteifen to keep alpha receptors clean, it's a pain in the ass. I love stimulants, but never again for Clen.
Not to mention it also thickens cardiac walls, causing hardening of heart muscles.
GW, Albuterol, Ephedrine, etc. are all MUCH better choices in my opinion. Don't worry though, I'm sure more vets will chime in on this as the evening progress, and confirm pretty much what I've said already.