If ephedrine cannot be obtained, pseudoephedrine, ephedrine's optical isomer, can be substituted in. Contrary to popular belief studies have shown pseudoephedrine to have a thermogenic effect; approximately three times less than L-ephedrine. Therefore, three Sudafed tablets, or 90 mg pseudoephedrine should provide approximately the same thermogenic effect as 25 mg ephedrine, but the overall effects of a pseudoephedrine based stack compared to an ephedrine based stack have not been studied (it is unlikely that PSE would produce an anoretic effect due to the low CNS activity, which is responsible for ~75% of the ECA stack's weight loss).