Doeth good like a medicine - Better, worketh a good healing. Omit "like."

A merry heart doeth good like a medicine - Instead of גהה gehah, a medicine, it appears that the Chaldee and Syriac had read in their copies גוה gevah, the body, as they translate in this way. This makes the apposition here more complete: "A merry heart doeth good to the body; but a broken spirit drieth the bones." Nothing has such a direct tendency to ruin health and waste out life as grief, anxiety, fretfulness, bad tempers, etc. All these work death.

A merry heart doth good like a medicine,.... Does the body good, makes it healthful and vigorous. Cheerfulness of spirit has a great influence upon the body, and much contributes to the health and welfare of it; see Ecclesiastes 9:7; and especially a heart full of spiritual joy, peace of conscience, flowing from the blood of Christ, joy in the Holy Ghost, a rejoicing in Christ Jesus and his righteousness, and in hope of the glory of God, much affect even the outward man. Or, "a merry heart makes a good medicine" (x); it is a good medicine of itself; raises the spirits, invigorates the body, and fits it for service and business: or, "does a medicine good" (y); makes that operate kindly, and to a good purpose: or, as Jarchi, makes the countenance shine well, makes a serene countenance; which Schultens approves, and, from the use of the word in the Arabic language, confirms;
but a broken spirit drieth the bones; a spirit broken with sorrow, whether on spiritual or temporal accounts; as it weakens the nerves, it dries up the marrow in the bones, and emaciates the body, and reduces it to a skeleton: the joy or grief of the mind, those passions of the soul, have a very great influence upon the body, either for its good or hurt.
(x) "cor hilare bonam facit sanationem", Michaelis. (y) So R. Joseph Kimchi; "bonificat sive meliorem reddit medicinam", some in Valablus; "bene medicinam facit", Junius & Tremellius, Piscator.

It is great mercy that God gives us leave to be cheerful, and cause to be cheerful, if by his grace he gives us hearts to be cheerful.

(Compare Proverbs 14:30; Proverbs 15:13). The effect of the mind on the body is well known.
medicine--or, "body," which better corresponds with "bone."
drieth--as if the marrow were exhausted.

22 A joyful heart bringeth good recovery;
And a broken spirit drieth the bones.
The heart is the centre of the individual life, and the condition and the tone of the heart communicates itself to this life, even to its outermost circumference; the spirit is the power of self-consciousness which, according as it is lifted up or broken, also lifts up or breaks down the condition of the body (Psychol. p. 199), vid., the similar contrasted phrases לב שׂמח and רוּח נכאה, Proverbs 15:13. The ἄπ. λεγ. גּהה (here and there in Codd. incorrectly written גּיהה) has nothing to do with the Arab. jihat, which does not mean sight, but direction, and is formed from wjah (whence wajah, sight), like עדה, congregation, from ועד (יעד). The Syr., Targ. (perhaps also Symmachus: ἀγαθύνει ἡλικίαν; Jerome: aetatem floridam facit; Luther: makes the life lstig [cheerful]) translate it by body; but for this גּוה (גּויּה) is used, and that is a word of an entirely different root from גּהה. To what verb this refers is shown by Hosea 5:13 : ולא־יגהה מכּם מזור, and healed not for you her ulcerous wound. מזור is the compress, i.e., the bandage closing up the ulcer, then also the ulcer-wound itself; and גּהה is the contrary of עלה, e.g., Jeremiah 8:22; it means the removing of the bandage and the healing of the wound. This is confirmed by the Syr. gho, which in like manner is construed with min, and means to be delivered from something (vid., Bernstein's Lex. Syr. to Kirsch's Chrestomathie). The Aethiop. quadriliteral gâhgěh, to hinder, to cause to cease, corresponds to the causative Syr. agahish. Accordingly גּהה means to be in the condition of abatement, mitigation, healing; and גּהה (as synonym of כּהה, Nehemiah 3:19, with which Parchon combines it), levamen, levatio, in the sense of bodily healing (lxx εὐεκτεῖν ποιεῖ; Venet., after Kimchi, ἀγαθυνεῖ θεραπείαν); and היטיב גּהה (cf. Proverbs 15:2) denotes, to bring good improvement, to advance powerfully the recovery. Schultens compares the Arab. jahy, nitescere, disserenari, as Menahem has done ננהּ, but this word is one of the few words which are explained exclusively from the Syriac (and Aethiop.). גּרם (here and at Proverbs 25:15) is the word interchanging with עצם, Proverbs 15:30; Proverbs 16:24.

Doth good - Even to the body; it contributes much to bodily health and vigour. Drieth - Wastes the marrow of the bones, and the moisture and strength of the body.