In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Although there were significant improvements relative to baseline in sexual desire and orgasm intensity / pleasure on 50 mg ephedrine 1 - hr prior to sexual activity , significant improvements in these measures , as well as in sexual arousal and orgasmic ability also were noted with placebo .
### Output Text:
Although there were significant improvements relative to baseline in sexual desire and orgasm intensity / pleasure on 50 mg <span class="chemical">ephedrine</span> 1 - hr prior to sexual activity , significant improvements in these measures , as well as in sexual arousal and orgasmic ability also were noted with placebo . 