The following two passages are from the Mirabilia of Apollonius the Paradoxographer (usually dated to the 2nd Century BCE, making him one of the earliest extant paradoxographers).
This plant makes you bigger [=BNJ 81 F17]
“Phularkhos writes in the eighth book of his Histories that near the Arabian Gulf there is a spring of water from which if anyone ever anoints their feet what transpires miraculously is that their penis becomes enormously erect. For some it never contracts completely, while others are put back in shape with great suffering and medical attention.”
14 Φύλαρχος ἐν τῇ η′ τῶν ἱστοριῶν [καὶ] κατὰ τὸν ᾿Αράβιόν φησι κόλπον πηγὴν εἶναι ὕδατος, ἐξ οὗ εἴ τις τοὺς πόδας χρίσειεν, συμβαίνειν εὐθέως ἐντείνεσθαι ἐπὶ πολὺ τὸ αἰδοῖον, καί τινων μὲν μηδ’ ὅλως συστέλλεσθαι, τινῶν δὲ μετὰ μεγάλης κακοπαθείας καὶ θεραπείας ἀποκαθίστασθαι.
This plant makes you smaller [=BNJ 81 F35a]
“Phularkhos in book 20 of the Histories says that there is a white root imported from India which when [people] cut it and smear it over their feet with water, those who are smeared with it experience forgetfulness of sex and become similar to Eunuchs. For this reason still some apply it before they are fully adults and are not aroused for the rest of their life.”
18 Φύλαρχος ἐν <τῇ> κ′ τῶν ἱστοριῶν ἐκ τῆς ᾿Ινδικῆς φησιν ἐνεχθῆναι λευκὴν ῥίζαν, ἣν κόπτοντας μεθ’ ὕδατος καταπλάττειν τοὺς πόδας, τοὺς δὲ καταπλασθέντας ἄνδρας τῆς συνουσίας λήθην ἴσχειν καὶ γίγνεσθαι ὁμοίους εὐνούχοις. διὸ καὶ ἔτι ἀνήβων ὄντων καταχρίουσι καὶ μέχρι θανάτου οὐκ ἐπαίρουσιν.
This anecdote has a later parallel from Athenaeus
Athenaeus, Deipn. 1.32 [=BNJ8135b]
“Phularkhos says that Sandrokottos, the king of the Indians, sent along with other gifts to Seleukos some drugs with erectile powers, the kind of which, when they are applied beneath feet of those who are going to have sex, give the the urge like birds, while some people lose their ability [for sex].”
Φύλαρχος δὲ Σανδρόκοττόν φησι τὸν ᾽Ινδῶν βασιλέα Σελεύκωι μεθ᾽ ὧν ἔπεμψε δώρων ἀποστεῖλαί τινας δυνάμεις στυτικὰς τοιαύτας ὡς ὑπὸ τοὺς πόδας τιθεμένας τῶν συνουσιαζόντων οἷς μὲν ὁρμὰς ἐμποιεῖν ὀρνίθων δίκην, οὓς δὲ καταπαύειν.
Phularkhos (Phylarchus) is an Athenian historian from the 3rd century BCE known for his love of anecdote and miraculous detail
Here is an ancient spell for erectile dysfunction (go here for translation note):
Magical Papyri, 7.185
“To be able to fuck a lot: mix fifty [pine nuts] with two measures of honey and seeds of pepper and drink it. To have an erection whenever you want: mix pepper with honey and rub it on your thing.”
Πολλὰ βι[ν]εῖν δύνασθαι· στροβίλια πεντήκοντα μετὰ δύο κυά[θ]ων γλυκέος καὶ κόκκους πεπέρεως τρίψας πίε. Στ[ύ]ειν, ὅτε θέλεις· πέπερι μετὰ μέλιτος τρίψας χρῖέ σου τὸ πρᾶ̣γ̣μ̣α.
