"Skeletal muscle contains all three β -adrenoceptor subtypes ( β 1, β 2 and β 3), with about a 10-fold greater proportion of the β 2-adrenoceptor isoform than β 1 or β 3 receptors [
30,
31]. The expression of subtype receptors remains to be checked under denervation condition in the future studies. Conversely, cardiac muscle contains approximately more than twofold of β 1-adrenoceptors than β 2 [
1]. This forms a theoretic basis for adjusting doses of β 2 agonists to affect skeletal rather than myocardial muscles. Indeed, proper dosages of β 2 agonists, such as clenbuterol, separate the effects on different types of muscles in patients [
9–
11]. Among the known β 2 agonists, clenbuterol appears to have the safest cardiac profile. To elaborate, clenbuterol given at 1000 μ g/kg/day, caused no myocardial hypertrophy in rats, but rather skeletal muscle hypertrophy [
32]. Consistently, clenbuterol (up to 720 μ g/day) promotes cardiac recovery in patients with left ventricular unloading atrophy [
12–
14].
Physiological dose of clenbuterol in rats, 10 μ g/kg/day, attenuated denervated muscle atrophy without affecting the heart or causing myocyte death [
25,
34]. That dosage was calculated based on the metabolic body weight that 10 μ g/kg/day in rats is equivalent to 1 μ g/kg/day in humans, a dose safely used in asthma treatments [
25,
35]. The dose in the current study was 120 μ g/day (~2 μ g/kg/day for a 60 kg person). It was well tolerated and not associated with any obvious discomfort, except for one patient with transient nervousness. The newly occurring sinus bradycardia after the clenbuterol trial seemed not be relevant to the activation of the β 1/2 agonist, which usually leads to tachycardia. Moreover, clenbuterol at the present dose did not exacerbate preexisting minor EKG abnormalities. This is consistent with previous reports that the effects of clenbuterol on the heart are observable at a dose of up to 2100 μ g/day in combination therapy for patients using left ventricular assist device. Even at those doses, no severe adverse effects were encountered but tremors and muscle cramps [
12,
13]. In our study, no adverse effects on liver, kidneys, lungs or hematopoietic system were observed after the 3-month intake of clenbuterol.
This pilot single-center study was small in scale. The efficacy would be more apparent in a larger patient population with either gradual increments of clenbuterol doses, or an on and off schedule to avoid the occurrence of receptor desensitization. Recent animal studies also show that clenbuterol is neuroprotective and promotes axon regeneration [
5,
28,
29]. Thus, in combination with its antiatrophy function, clenbuterol and its kind truly represent promising and safe agents for countering nerve injuries."
This is from an actual study, Not a case report.
Clen is used for Asthma treatment in many eastern euro countries, as well as in Mexico.
Ghoul on the meso forum summarizes it really well
"
I've used clen for as long as 8 months. Off now.
I'll make the key points succinctly, if you need more details lmk.
"Tolerance" does develop quickly but it's not that simple. Metabolically 80mg of Clen, without prior use, will increase resting calorie burn by 29%, and fat lipolysis (breakdown to fatty acids) by 39%, along with increasing insulin sensitivity and other fat loss enhancing effects.
The tolerance that quickly develops primarily affects the tremors and boosted twitch speed of muscles. This accounts for only a portion of the extra resting calorie burn, and quickly diminishes as you take the same dose. Some users think that's an indication it's no longer working, which isn't accurate. I also thought increased doses to keep the tremors going and the break to reset receptors were necessary to restore the fat loss effects after you reached your max dose and the tremors stopped, but that wasn't actually necessary.
The increased fat metabolism is a direct action of Clen on fat cells, not relying on continued beta receptor sensitivity.
Air passages continue to be opened more than normal, resulting in higher resting calorie burn.
After all, when used as an asthma med it would be taken for years at the same dose. The tremors are considered a temporary side effect when treatment is initiated. No "break" or ever increasing dose is required to keep patients breathing more easily, or as we're trying to induce, additional fat oxidation.
The increased insulin sensitivity is so durable Clen has experimentally been used as a treatment for diabetes. Again, this doesn't fade with tolerance.
So do you lose some of the "free" calorie burn from a lack of tremors and muscles that have increased twitch response? Yes, how much? Not enough to warrant repeatedly going through the stress the tremor stage puts on your body in as you keep cycling over an extended period, in my opinion. The time to reset receptor sensitivity varies from person to person and protocols are all over the place, btw.
Most of the fat loss benefits will continue with sustained use, and the only way to go if you want to use this for a long period to counteract your slowed metabolism. Do something else to burn off what is perhaps 100-200 / day in extra calories from the tremor stage. The biggest benefits are the continuing enhanced lipolysis that will speed fat loss and boost energy, and better glucose control from increased insulin sensitivity. That is largely what "better metabolism" is anyway right?
So for dosing. 40ug twice a day is the asthma dose, proven to be safe for long term use. 80ug twice a day is the highest amount I've found referred to in a long term study (6 months), and those were people weakened by ALS, with no ill effects.
Because of the possible unintentional overdosing with UGL Clen I wouldn't go past 80ug a day, and would usually take that in one dose early in the morning, A split dose is better but no later than noon for the second to avoid insomnia. With pharma I'd be comfortable going up to 80ug twice a day max. Thats me, 40ug twice a day will still be effective. This is all after slow titration and dependent on how you respond. Don't go higher if you don't feel well. You've also got to monitor BP as it can drop too low if you're normal or below already. First time use 20ug for 4 days, then 40ug, 60ug, until you reach your max. Increasing every 4 days or when the tremors ease off.
Although plenty of people have gone to the hospital after taking too much, or ingesting it accidentally (an infant ate 20 tabs, and turned out ok thankfully) or it was used to cut street drugs, documented injury has only been recorded at really high doses, and thankfully very rare. No fatalities as far as I've been able to find. Definitely don't play with raws. It's essentially heart muscle damage from increased heart rate combined with insufficient oxygen supply from the low blood pressure. Again, the highest heart rate is in the tremor stage when the receptors are most sensitive, so even though the doses we're talking about shouldn't put you anywhere near the danger zone, it's another reason to not cycle back into the tremors.
Stay really well hydrated. A lot of the extra energy expenditure is going to be from expelling moisture via breathing. So not only is dehydration bad in general, it'll slow fat loss.
Your heart isn't going nuts, so the hazard of an overworking heart suffering from oxygen depravation damaging muscle cells drops precipitously. Probably back to near zero, or whatever it would normally be without clen.
There's no mysterious effect clen has that damages the heart. Your heart rate speeds up, blood pressure goes down, and if it beats too fast, for too long, the oxygen supplied by blood flow is insufficient to meet its heightened needs and some heart muscle cells die from oxygen depravation. However, this only happens at epic doses, and while the receptors are sensitive. Assuming you don't have some underlying heart issues.
"
So not trying to argue, just providing you with some information that may make you change your mind. ALSO keep in mind that many Glucagon based drugs never made it to market BECAUSE of the cardiac concerns of chronic glucagon agonism. Pretty crazy they gave people 720mcg of Clen in a medical setting, and they did not notice any significant negatives.
ClinicalTrials.gov
clinicaltrials.gov
Randomized, Double-Blind, and Placebo-Controlled Trial of Clenbuterol in Denervated Muscle Atrophy - PMC
Objectives. β 2-adrenergic agonists, such as clenbuterol, have been shown to promote the hypertrophy of healthy skeletal muscles and to ameliorate muscle wasting in a few pathological conditions in both animals and humans. We intended to investigate ...
pmc.ncbi.nlm.nih.gov
https://thinksteroids.com/community/threads/how-long-can-i-take-clen-for.134425376/page-2#posts
If I had to be on a Rx-level stimulant, I would choose modafinil, but it is a controlled substance, so non-zero legal risk for sourcing from India.
