Placebo is a name for procedures and drugs that have no direct effect. They might have indirect effects, such as alleviating anxiety by convincing the patient that you are taking care of them. Or, it might just be indirect effects where people try to be helpful and report some improvement in their conditions, even if none has occurred. Or, it might just be reporters fudging the data to support the medicine's effectiveness. They may also change patient behavior through effects such as 'sunk cost' or more complex ones, like circumcision possibly reducing sexual pleasure, therefore decreasing the chance of risky sexual behavior.

But there is 0 evidence of placebos having actual positive effects aprt from the first one about subjective symptoms.