I think your first instinct is the best. Be up front about it then there is no surprise if positive. Same is true if you have been eating poppy seed muffins. Drug tests are given post offer, pre-eployment. They can't have you take the drug test unless they have offered you a position. If you fail the test they can revoke the offer. Best to tell them upfront about the cocoa tea then if you test positive for that substance you can provide verification of your placement with host family in Peru. Inform the facility of any drugs you are taking so they can exclude any positives for those drugs.
What the testing facility reports depends on the agreement you sign. If your offer is revoked due to failed drug test it shouldn't have any effect on future employment, except if an application specifically asks you about it. (Not typical). Never lie on an application by omission or commission, you can be terminated for cause for doing so, and for cause terminations usually result in denial of unemployment benefits.
Consult with a local employment attorney for your home state laws and regulations.
All the best.
NO LEGAL ADVICE GIVEN. READ THIS BEFORE you contact me! My responses to questions on Avvo are never intended as legal advice and must not be relied upon as if they were legal advice. I give legal advice ONLY in the course of a formal attorney-client relationship set forth in a written document executed by the client and by me or a member of my firm. Exchange of information through Avvo's Questions forum does not establish an attorney-client relationship with me. My law firm does NOT provide free consultations. Please do not call or write to me with a “few questions” that require me to analyze the specific facts of your history and your case. I can give advice, make recommendations and answer specific questions only after reviewing the evidence and documents applicable to a specific client and following a personal meeting in my office in which the relevant facts can be developed and analyzed. My law firm presently accepts cases involving State and federal administrative law; professional licenses and permits; education law; employment and labor law; and litigation matters in state and federal courts. Our practice is limited to the States of Oregon and California. If you have a case in any other state we would not be able to assist you. Unless we have a signed written fee agreement you are not my or my firm's client.
Depends how long ago this was? if it was more than a week or two ago, don't worry about it unless the test is hair.
In accordance with the Avvo community guidelines, this communication does not constitute "legal advice", nor does it form an attorney-client relationship. You should seek counsel in your geographic area regarding any specific questions.